ECM Constants
08-17-2003, 12:44 PM
#1
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ECM Constants
More changes and edits. 
This is the ECM constants as seen in tunercat...
Cylinder volume: Expressed in millileters per cylinder.
*Here are a couple of formulas to get you the correct value to put here:
Cubic Inches / 61.5 = Liters
Liters x 1000 = Milliliters
Milliliters / Number of Cylinders = Milliliters per Cylinder
Injector Flow Rate (Injector Constant):
For the stock 24lb injector GM has set this value to 24.91.
To figure this for injectors other than stock you need to take the square root of your fuel pressure divided by the pressure the injectors were rated at, then multiply by the size of injector. Example, if you still have the stock fuel pressure regulator on your car, the LT1 fuel system operates at ~43.5psi.
Now to figure the injector constant for a Ford/SVO 30lb injector you'd take the square root of 43.5/39 and then multiply by 30 and end up with a value of 31.68. The 39 represents the pressure at which Ford/SVO injectors flow was rated at.
This can also be applied to other fuel injectors if you know what pressure they were rated at.
MAP Threshold to Enable WOT:
This is the minimum map value that the computer must see in order to declare wide open throttle.
EGR enable controls: If you’re keeping the EGR system, leave these tables stock.
If you’ve removed the EGR system, the easiest way to disable it is to set the EGR enable minimum rpm to a very high rpm, or the EGR enable maximum rpm really low.
Fan thresholds:
These are the engine coolant temperatures that the ECM must see in order to kick the fans on. For the stock 180* thermostat the fan turn on points are 226 for the low speed and 235 for the high speed. A good starting point for either the stock or an aftermarket 160* thermostat is to set the low speed fan to come on 20* after the thermostat has opened, and the high speed to come on 6-8* after the low speed. It is best to experiment and see what you‘re car likes best. Use the Fan 1 On Threshold (Low MPH) and the Fan 2 On Threshold (Low MPH) for your turn on temperatures.
The Fan Threshold High Speed (MPH) allows you to give the computer a mph value to distinguish between the high and low speed fan turn on points. This gets pretty interesting.
For example, you drive a lot in stop and go traffic and are consistently driving at 35mph and under. You can set your high speed threshold to 35mph and then at every speed under that the low mph fan turn on temps are active, and at any speed higher than that the high mph fan turn on temps are active. That way you can kick the fans on earlier at lower speeds to make up for the lack of airflow coming across the radiator while you‘re sitting in traffic. Then once your at a speed that allows the radiator to see more airflow the high speed turn on temps take control.
Fan Hysteresis Low/High Speed: These values are the temperature changes that will turn the fans off. If you’ve set the hysteresis to 3, then the fans will not turn off until the coolant temperature is 3 degrees cooler than the fans turn on point.
Fan control turn-on points based on oil temp are not used in our ECM’s since it takes no input of oil temp.
There are also values for fan turn-ons based on A/C pressure. I have not messed with these values as I don‘t see an advantage to it.
Fuel Cut-Off and Resume Speed: This is a MPH based setting that is your speed limiter.
Fuel Cut-Off and Resume Rev Limiter: This is the RPM based setting that allows you to change your rev-limiter.
VSS Diagnostic Enable Minimum RPM:
Not sure exactly what this does, but I’ve been wondering if you set the rpm on this to it’s maximum value if the computer would not be able to activate the limp mode that causes the OBDI 1st-2nd shift problem. I’ve always been under the assumption that the no-shift is caused be a hard launch on sticky tires that would cause the VSS to lose it’s signal and set the trans into limp mode.
Try it and see if it works for you.
CARS or the Skip Shift Funtion: The easiest way to disable this is to set the enable rpm to it’s maximum value. Skip shift disabled.
Low PRNDL Upshift/Downshift Speed Threshold:
These tables are used when you select 1st gear manually on the shifter. If you set the Upshift Constant to 35mph the computer will automatically shift the car into 2nd gear at 35mph even if the shifter is left in 1st. Excellent as a safety feature.
Set the Downshift Constant to a value lower than the Upshift. If you set the downshift to 20mph and try to downshift the car into 1st at a speed higher than that, the computer will not let the car downshift.
Maximum Line Pressure: This is the maximum amount of transmission line pressure that is allowable on the A4 cars. I think that this value can not be over-ridden by the other transmission tables.
Kickdown Mode Enable/Disable TPS Threshold: These are the TPS values that are used to activate the kick down mph and rpm tables that control wide open throttle shift points.
Minimum Coolant Temp for Closed Loop: This is the minimum coolant temperature that the car will switch from open loop to closed loop.
Minimum and Maximum BLM: These are the highest and lowest block learn multiplier values that the computer will use in order to adjust its fueling requirements.
BLM Cell Map Boundary Hysteresis and BLM Cell RPM Boundary Hysteresis:
The BLM table has boundaries for both RPM and MAP. These boundaries determine where on the grid (which BLM Cell) your sitting at.
Stock BLM Cell MAP Bounadary is: Low 32, Mid 50, High 80.
Stock Cell RPM boundary is: Low 700, Mid 1200, High 2000.
Example: Suppose though your crusing right around 1200 RPM and going slightly above and below it... so suppose your doing say 1175, 1200, 1225, 1200, 1175, 1200 etc. You don't want the computer constantly switching boundaries. These two hystersis settings come into play here. in order for you to be "IN" one of these cells you must leave another cell by an amount over the hysterisis value. For either the MAP or RPM. This is used similar to fan hysterisis - you don't want your fans switching on and off rapidly as your engine temp goes above and below a certain value all the time, so you give it a hysterisis value of a few degrees celcius.
DFCO Enable RPM Threshold and Enable Map Threshold: These 2 values are really used together to activate the deceleration fuel cut out mode. If engine rpm is above the RPM threshold and MAP is above the MAP threshold when you let off the gas and TPS goes to zero then DFCO will engage.
DFCO Disable RPM Threshold and Disable Map Threshold: These are the 2 values that will disable DFCO. They don’t need to work together like the enable values for this feature so if either is obtained DFCO disables.
DFCO Disable RPM Decrease Threshold: This is an rpm based value that if the car decelerates faster than, DFCO will disable.
DFCO Enable Coolant Temp Threshold: The is the coolant temperature that the car must reach before it can activate DFCO.
DFCO Enable MPH Threshold: This is the speed that the car must be above for DFCO to activate.
DFCO Spark Retard: This is the amount of spark retard that the computer will use in order to slow the car down when DFCO is enabled.
Knock Retard Enable Coolant Temp: This is the minimum engine coolant temperature that the computer will start to retard timing when it gets input from the knock sensor.
Burst Knock Enable % Difference Air Threshold: I think that this is the percentage of airflow difference (measured by the maf sensor?) that the computer must see to enable burst knock.
Burst Knock Enable Coolant Temperature Threshold: This is the coolant temperature that the car reach before burst knock can be enabled.
There are other constants shown in Tunercat and if anyone wants to add anything or if any of the above information is incorrect, please let me know.
And to those of you who have contributed information to this...Thank you!
This is the ECM constants as seen in tunercat...
Cylinder volume: Expressed in millileters per cylinder.
*Here are a couple of formulas to get you the correct value to put here:
Cubic Inches / 61.5 = Liters
Liters x 1000 = Milliliters
Milliliters / Number of Cylinders = Milliliters per Cylinder
Injector Flow Rate (Injector Constant):
For the stock 24lb injector GM has set this value to 24.91.
To figure this for injectors other than stock you need to take the square root of your fuel pressure divided by the pressure the injectors were rated at, then multiply by the size of injector. Example, if you still have the stock fuel pressure regulator on your car, the LT1 fuel system operates at ~43.5psi.
Now to figure the injector constant for a Ford/SVO 30lb injector you'd take the square root of 43.5/39 and then multiply by 30 and end up with a value of 31.68. The 39 represents the pressure at which Ford/SVO injectors flow was rated at.
This can also be applied to other fuel injectors if you know what pressure they were rated at.
MAP Threshold to Enable WOT:
This is the minimum map value that the computer must see in order to declare wide open throttle.
EGR enable controls: If you’re keeping the EGR system, leave these tables stock.
If you’ve removed the EGR system, the easiest way to disable it is to set the EGR enable minimum rpm to a very high rpm, or the EGR enable maximum rpm really low.
Fan thresholds:
These are the engine coolant temperatures that the ECM must see in order to kick the fans on. For the stock 180* thermostat the fan turn on points are 226 for the low speed and 235 for the high speed. A good starting point for either the stock or an aftermarket 160* thermostat is to set the low speed fan to come on 20* after the thermostat has opened, and the high speed to come on 6-8* after the low speed. It is best to experiment and see what you‘re car likes best. Use the Fan 1 On Threshold (Low MPH) and the Fan 2 On Threshold (Low MPH) for your turn on temperatures.
The Fan Threshold High Speed (MPH) allows you to give the computer a mph value to distinguish between the high and low speed fan turn on points. This gets pretty interesting.
For example, you drive a lot in stop and go traffic and are consistently driving at 35mph and under. You can set your high speed threshold to 35mph and then at every speed under that the low mph fan turn on temps are active, and at any speed higher than that the high mph fan turn on temps are active. That way you can kick the fans on earlier at lower speeds to make up for the lack of airflow coming across the radiator while you‘re sitting in traffic. Then once your at a speed that allows the radiator to see more airflow the high speed turn on temps take control.
Fan Hysteresis Low/High Speed: These values are the temperature changes that will turn the fans off. If you’ve set the hysteresis to 3, then the fans will not turn off until the coolant temperature is 3 degrees cooler than the fans turn on point.
Fan control turn-on points based on oil temp are not used in our ECM’s since it takes no input of oil temp.
There are also values for fan turn-ons based on A/C pressure. I have not messed with these values as I don‘t see an advantage to it.
Fuel Cut-Off and Resume Speed: This is a MPH based setting that is your speed limiter.
Fuel Cut-Off and Resume Rev Limiter: This is the RPM based setting that allows you to change your rev-limiter.
VSS Diagnostic Enable Minimum RPM:
Not sure exactly what this does, but I’ve been wondering if you set the rpm on this to it’s maximum value if the computer would not be able to activate the limp mode that causes the OBDI 1st-2nd shift problem. I’ve always been under the assumption that the no-shift is caused be a hard launch on sticky tires that would cause the VSS to lose it’s signal and set the trans into limp mode.
Try it and see if it works for you.
CARS or the Skip Shift Funtion: The easiest way to disable this is to set the enable rpm to it’s maximum value. Skip shift disabled.
Low PRNDL Upshift/Downshift Speed Threshold:
These tables are used when you select 1st gear manually on the shifter. If you set the Upshift Constant to 35mph the computer will automatically shift the car into 2nd gear at 35mph even if the shifter is left in 1st. Excellent as a safety feature.
Set the Downshift Constant to a value lower than the Upshift. If you set the downshift to 20mph and try to downshift the car into 1st at a speed higher than that, the computer will not let the car downshift.
Maximum Line Pressure: This is the maximum amount of transmission line pressure that is allowable on the A4 cars. I think that this value can not be over-ridden by the other transmission tables.
Kickdown Mode Enable/Disable TPS Threshold: These are the TPS values that are used to activate the kick down mph and rpm tables that control wide open throttle shift points.
Minimum Coolant Temp for Closed Loop: This is the minimum coolant temperature that the car will switch from open loop to closed loop.
Minimum and Maximum BLM: These are the highest and lowest block learn multiplier values that the computer will use in order to adjust its fueling requirements.
BLM Cell Map Boundary Hysteresis and BLM Cell RPM Boundary Hysteresis:
The BLM table has boundaries for both RPM and MAP. These boundaries determine where on the grid (which BLM Cell) your sitting at.
Stock BLM Cell MAP Bounadary is: Low 32, Mid 50, High 80.
Stock Cell RPM boundary is: Low 700, Mid 1200, High 2000.
Example: Suppose though your crusing right around 1200 RPM and going slightly above and below it... so suppose your doing say 1175, 1200, 1225, 1200, 1175, 1200 etc. You don't want the computer constantly switching boundaries. These two hystersis settings come into play here. in order for you to be "IN" one of these cells you must leave another cell by an amount over the hysterisis value. For either the MAP or RPM. This is used similar to fan hysterisis - you don't want your fans switching on and off rapidly as your engine temp goes above and below a certain value all the time, so you give it a hysterisis value of a few degrees celcius.
DFCO Enable RPM Threshold and Enable Map Threshold: These 2 values are really used together to activate the deceleration fuel cut out mode. If engine rpm is above the RPM threshold and MAP is above the MAP threshold when you let off the gas and TPS goes to zero then DFCO will engage.
DFCO Disable RPM Threshold and Disable Map Threshold: These are the 2 values that will disable DFCO. They don’t need to work together like the enable values for this feature so if either is obtained DFCO disables.
DFCO Disable RPM Decrease Threshold: This is an rpm based value that if the car decelerates faster than, DFCO will disable.
DFCO Enable Coolant Temp Threshold: The is the coolant temperature that the car must reach before it can activate DFCO.
DFCO Enable MPH Threshold: This is the speed that the car must be above for DFCO to activate.
DFCO Spark Retard: This is the amount of spark retard that the computer will use in order to slow the car down when DFCO is enabled.
Knock Retard Enable Coolant Temp: This is the minimum engine coolant temperature that the computer will start to retard timing when it gets input from the knock sensor.
Burst Knock Enable % Difference Air Threshold: I think that this is the percentage of airflow difference (measured by the maf sensor?) that the computer must see to enable burst knock.
Burst Knock Enable Coolant Temperature Threshold: This is the coolant temperature that the car reach before burst knock can be enabled.
There are other constants shown in Tunercat and if anyone wants to add anything or if any of the above information is incorrect, please let me know.
And to those of you who have contributed information to this...Thank you!
Last edited by Dan K; 04-03-2006 at 01:38 PM.
08-17-2003, 07:47 PM
#3
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Join Date: Jun 2003
Location: florida
Posts: 38
fan setting
that is the tempreture differential between on and off.
if you set the fan threshold at 120 and you fan hysteresis at 6
your fan wil come on at 120 degrees and will not shut off until your temp reaches 120 - 6(hys) . so it will shut the fan off at 114 degrees. the used temps are for example only. this should be the formula for both fans.
if you set the fan threshold at 120 and you fan hysteresis at 6
your fan wil come on at 120 degrees and will not shut off until your temp reaches 120 - 6(hys) . so it will shut the fan off at 114 degrees. the used temps are for example only. this should be the formula for both fans.
08-18-2003, 03:00 PM
#4
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Join Date: Mar 1999
Location: Vancouver BC, Canada
Posts: 528
1) Rev Limiter: This setting is based on mph and is pretty self explanatory.
Shouldn't that read 'based on rpm' rather then mph?
2)Knock Retard Enable Coolant Temp: Pretty self explanatory.
I may be a dumbass, but I don't know what that means Does it mean, Knock Retard is enabled by coolant temp? So only when the coolant temp gets to a certain range, will the computer be able to pull timing based on the knock sensors input? *shrug*
But great work Dan!
Thanks alot!
Jeff
Shouldn't that read 'based on rpm' rather then mph?
2)Knock Retard Enable Coolant Temp: Pretty self explanatory.
I may be a dumbass, but I don't know what that means
Does it mean, Knock Retard is enabled by coolant temp? So only when the coolant temp gets to a certain range, will the computer be able to pull timing based on the knock sensors input? *shrug*But great work Dan!
Thanks alot!
Jeff
08-18-2003, 04:42 PM
#5
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Join Date: Jul 2002
Location: Phoenix, AZ
Posts: 1,277
DFCO (Decel. Fuel Cut Off)constants. These are simple but very cool. I like mine giving my lotsa compression braking by reducing my timing retard. This makes the very lean AFR within the cylinder fire before optimal thus causing the car to brake instead of speed up. The other DFCO's are self explanatory regarding when DFCO engages and disengages.
Oh, and Dan, I challenge you to find out about when and why the hell low octane constants and tables are used. I have no clue.
Ben
Oh, and Dan, I challenge you to find out about when and why the hell low octane constants and tables are used. I have no clue.
Ben
08-19-2003, 12:40 AM
#6
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Location: so close I can taste it...
Posts: 1,009
Originally posted by JeffK95Z
1) Rev Limiter: This setting is based on mph and is pretty self explanatory.
Shouldn't that read 'based on rpm' rather then mph?
1) Rev Limiter: This setting is based on mph and is pretty self explanatory.
Shouldn't that read 'based on rpm' rather then mph?
2)Knock Retard Enable Coolant Temp: Pretty self explanatory.
I may be a dumbass, but I don't know what that means
I may be a dumbass, but I don't know what that means
Ben,
Would you mind writing up just a little explanation of what you'd like me to add as far as the DFCO stuff? Can you explain what each constant is? Cause I have no idea.
And no, I won't take your challenge right now.
Maybe later.
08-25-2003, 04:34 PM
#9
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Location: Cincinnati, OH, USA
Posts: 1,009
For people with different cams, the Closed TPS timing table is good to know.
You can set your idle timing with this as well as coast-down timing. Increasing tends to help with cams with more overlap, if I remember correctly.
You can set your idle timing with this as well as coast-down timing. Increasing tends to help with cams with more overlap, if I remember correctly.
08-25-2003, 07:36 PM
#10
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Join Date: Jul 2001
Location: so close I can taste it...
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Originally posted by JSK333
For people with different cams, the Closed TPS timing table is good to know.
You can set your idle timing with this as well as coast-down timing. Increasing tends to help with cams with more overlap, if I remember correctly.
For people with different cams, the Closed TPS timing table is good to know.
You can set your idle timing with this as well as coast-down timing. Increasing tends to help with cams with more overlap, if I remember correctly.
08-25-2003, 10:06 PM
#11
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Location: Cincinnati, OH, USA
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Sorry, I saw "constants" but it never dawned on me what you meant by it. 
I have a guess on the "Low PRNDL..." constant. I have a feeling it has to do with how quickly gear changes in the A4 will engage at low speeds. Probably to prevent harsh engagements from reverse->drive, and so on. I know I've driven some A4s that would snap the neck on the change, or squack the tires... this constant probably affects this.
I have a guess on the "Low PRNDL..." constant.
I have a feeling it has to do with how quickly gear changes in the A4 will engage at low speeds. Probably to prevent harsh engagements from reverse->drive, and so on. I know I've driven some A4s that would snap the neck on the change, or squack the tires... this constant probably affects this.
08-27-2003, 06:48 AM
#13
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Join Date: Feb 2000
Location: Cleveland,OH
Posts: 1,335
Originally posted by Dan K
TTT
No more comments on this? Anyone have anything to add? Correct?
Anything?
TTT
No more comments on this? Anyone have anything to add? Correct?
Anything?
08-27-2003, 11:30 AM
#14
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Join Date: Jan 2000
Location: Lockport, Illinois 60441
Posts: 487
Low PRNDL Upshift/Downshift Speed Threshold: I do not have any personal experience with this. But I have seen it set at different values in different files. If anyone knows exactly what this does and how it works, please let me know.
Upshift Threshold: This setting is for when you have the car selected in 1st gear manually, It is set by MPH. Say you enter it at 35 MPH. If your in first gear and hit 35, the computer will shift your trans into 2nd for you, even if you have the gear selector in 1st. I have tried it out. Its a safety feature to not over rev the engine.
Downshift Threshold: Just the opposite of what upshift is. If your cruising around 45 and try to downshift into first, It will not let the trans go down unless you are lower then the MPH this is set at. I wouldn't recommend downshifting your auto trans manually as its no good for the trans anyways.
Upshift Threshold: This setting is for when you have the car selected in 1st gear manually, It is set by MPH. Say you enter it at 35 MPH. If your in first gear and hit 35, the computer will shift your trans into 2nd for you, even if you have the gear selector in 1st. I have tried it out. Its a safety feature to not over rev the engine.
Downshift Threshold: Just the opposite of what upshift is. If your cruising around 45 and try to downshift into first, It will not let the trans go down unless you are lower then the MPH this is set at. I wouldn't recommend downshifting your auto trans manually as its no good for the trans anyways.
08-27-2003, 11:37 AM
#15
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Location: Lockport, Illinois 60441
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Originally posted by kevmor99
What is the fan hysteresis (shown in deg.C)?
What is the fan hysteresis (shown in deg.C)?